With the recent growing awareness of environmental preservation and concern about power shortage, a great deal of attention has been paid to a home energy management system (HEMS) or a distributed power supply such as a photovoltaic power generation (PV) system, storage battery, or fuel cell (FC) unit. Furthermore, attention has been paid to a zero energy home (ZEH) or net-zero energy home. The net-zero energy home indicates a home whose net primary energy consumption per year is almost zero.
Among distributed power supplies, a fuel cell is regarded as promising since it can stably generate power day and night in any weather conditions, and supply heat energy using exhaust heat. However, a reverse flow from a fuel cell to a commercial power grid is not permitted under contract with power companies. There have been proposed some techniques of preventing a reverse flow of power generated by a fuel cell.
Techniques associated with electric vehicles have been extensively developed. A battery mounted on the vehicle of this type has significantly progressed as compared with conventional batteries. It has been proposed to supply power to a home in case of a power failure or the like by taking advantage of such battery.
There is provided a technique of preventing a reverse flow by causing a dummy load or reverse flow prevention heater to consume dump power generated by a fuel cell. With this technique, energy is wasted. There is also a technique of storing dump power in a storage battery. However, when it becomes necessary to store power, the storage battery may have been fully charged to disable further charge.
Even if the reverse flow prevention heater and storage battery are used together, it takes long timer to change the output of the fuel cell. If, therefore, a period of time within which the power demand is low becomes long, a dump power generation amount unwantedly exceeds the capacity of a storage battery. In such case, there is no choice but to stop the operation of the fuel battery, or cause the reverse flow prevention heater to consume dump power. Even if a reverse flow can be prevented by isolating the fuel battery from the grid by a relay or the like, dump power is wasted under the present circumstances.
On the other hand, a combined technique of a HEMS and the on-vehicle battery of an electrical vehicle is under development. An energy management method which collectively considers electrical equipment in a home and an on-vehicle battery is particularly required.